Does Ozone Alter the Attractiveness of Japanese White Birch Leaves to the Leaf Beetle Agelastica coerulea via Changes in Biogenic Volatile Organic Compounds (BVOCs): An Examination with the Y-Tube Test

Noboru Masui,Evgenios Agathokleous,Akira Tani,Takayoshi Koike,Hideyuki Matsuura,Tomoki Mochizuki,Toshihiro Watanabe

doi:10.3390/f11010058

Abstract

Elevated ground-level ozone (O3) reduced C-based defense chemicals; however, severe grazing damages were found in leaves grown in the low O3 condition of a free air O3-concentration enrichment (O3-FACE) system. To explain this phenomenon, this study investigates the role of BVOCs (biogenic volatile organic compounds) as signaling compounds for insect herbivores. BVOCs act as scents for herbivore insects to locate host plants, while some BVOCs show high reactivity to O3, inducing changes in the composition of BVOCs in atmospheres with elevated O3. To assess the aforementioned phenomenon, profiles of BVOCs emitted from birch (Betula platyphylla var. japonica Hara) leaves were analyzed ex situ, and Y-tube insect preference tests were conducted in vitro to study the insect olfactory response. The assays were conducted in June and August or September, according to the life cycle of the adult alder leaf beetle Agelastica coerulea Baly (Coleoptera: Chrysomelidae). The Y-tube tests revealed that the leaf beetles were attracted to BVOCs, and O3 per se had neither an attractant nor a repellent effect. BVOCs became less attractant when mixed with highly concentrated O3 (>80 ppb). About 20% of the total BVOCs emitted were highly O3-reactive compounds, such as β-ocimene. The results suggest that BVOCs emitted from the birch leaves can be altered by elevated O3, thus potentially reducing the attractiveness of leaves to herbivorous insects searching for food.

Highlights

Ground-level ozone (O3 ) has been elevated in the last decades, especially in east Asia [1,2,3]
We investigated the changes in biogenic volatile organic compounds (BVOCs) under elevated O3 and how they potentially affect the grazing of the leaf beetle
The adult leaf beetles showed no preference/avoidance against O3 per se at any concentrations in test (1) O3 versus cleaned air (CA) containing no BVOCs (Figure 3a,b). They preferred BVOCs emitted from leaves of white birch trough CA in test (2) (Figure 3c; first generation: p < 0.05, second generation: p < 0.001)

Summary

Introduction

Ground-level ozone (O3 ) has been elevated in the last decades, especially in east Asia [1,2,3]. O3 is a strong oxidant at high concentrations, and can damage photosynthesis, growth, and development of plants [4,5]. O3 can enhance the susceptibility of plants to insect herbivores and diseases, potentially disrupting the disease triangle [6,7]. Forests 2020, 11, 58 from photosynthates; plant defense capacity can be decreased by elevated O3 concentrations [8]. This is important in rural and mountainous areas, where O3 levels are higher than in cities [9]. Damages by herbivores are responsible for losses of net primary production up to 15% in temperate forests [8]; herbivory can be altered by atmospheric contaminants. We have previously found that insect herbivores systematically grazed leaves of different tree species in ambient

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